Birds inhabit many diverse habitats on Earth, from the equator to the poles, on land and at sea. Few birds (less than 200 species worldwide) spend the majority of their time at sea. The rest remain close to land, where food is more concentrated.
are endothermic, sometimes called "warm blooded." This means that they can maintain their body temperature separately from their environment. Mammals keep themselves warm, which is different than a lizard that must bask in the Sun to get a warm body temperature.